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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Urgent question: malloc and ada...
Date: 1998/05/03
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Date: 1998-05-03T00:00:00+00:00
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Jonathan says

<<Actually, I was commenting more on the alignment of structs (which, as
far as I know, can vary even on those systems with a single calling
convention) than the calling convention.  Calling conventions are usually
reasonably well standardized, the alignment of structs is not.  Yet your
post implied that both are covered (as they would have to be) by the
requirements.
>>

I was using calling sequence quite generally here. The alignment of structs
is most CERTAINLY included, since part of what one does on a call is to pass
references to various kinds of data, and of course the alignment and layout of this
data must be clearly understood between callee and caller.

So most definitely the convention in the ADa sense *does* cover alignment
of structs. If two compilers differed in this respect, and an Ada compiler
wished to interface to both, then it would have to provide for this, either
by using separate calling conventions, or by using special pragmas.
THe use of separate calling conventions is preferable, since it avoids the
use of potentially non-portable pragmas. 

We still have not managed to coax out of Joe even one example of problems
in interfacing in a portable manner, but clearly if this is a goal (and it
was indeed a goal of the Ada 95 design), then it is better to stick to
the mechanisms provided in the RM. We deviated from this in GNAT/VMS
(providing the pragma Component_Alignment) since in this case, compatibility
with DEC Ada 83 is much more of an issue than compatibility with other
Ada 95 compilers, and indeed one would expect other Ada 985 compilers
for VMS to be driven by the same considerations in any case.